Blowing voltage regulators
It still should not jump voltage like that. Frankly for the "root" of this problem I'd suspect a partially shorted alternator field. Get yourself a shop manual, there's a procedure in there to measure field current draw.
And, I would not waste time re-engineering mechanical regulators. Most any aftermarket regulator you buy nowadays is going to be electronic in a mechanical case, so to speak.
You may have a loose / poor ground between VR and battery.